It is not known how many people regularly engage in chemsex in the UK, although a study found that 3,000 gay men a month attended sexual health clinics and reported using recreational drugs. Around 100 new patients a month, aged from 15 to 70, access 56 Dean Street's chemsex support service.
Stuart said: "Chemsex is a health syndemic that can't simply be left to substance misuse services to address. It requires cross-sector, multi-disciplinary partnership, resourcing sexual health professionals, mental health teams, a strong gay community and voluntary sector response, as well as the skills from substance misuse services."
While the use of psychoactive substances during sex is not a new phenomenon in London's gay scene, its use has grown alongside the increasing popularity of so-called hook-up apps such as Grindr. Some Grindr users advertise their willingness to take part in chemsex using the acronym 'H&H' - high and horny - and it is estimated that users in south London are likely to be offered drugs within four interactions on the app.
Andrew, 24, started attending chillouts at people's houses when he was 18. He said it was fun at first but they soon became "really sexually charged". "It just took a dark turn. I think I noticed what I was doing felt wrong when I felt quite pressured into consuming a lot of drugs and then having to have sex afterwards," he said.
"It made me voracious, like I couldn't stop, it's all I wanted to do. It wouldn't matter who they were, what they looked like, how old they were, if they were HIV-positive, Hep C positive - it made no difference to me."